.\" Copyright (c) 2007 Joseph Koshy.  All rights reserved.
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.Dd November 25, 2007
.Dt PMC_READ 3
.Os
.Sh NAME
.Nm pmc_read ,
.Nm pmc_rw ,
.Nm pmc_write
.Nd read and write hardware performance counters
.Sh LIBRARY
.Lb libpmc
.Sh SYNOPSIS
.In pmc.h
.Ft int
.Fn pmc_read "pmc_id_t pmc" "pmc_value_t *value"
.Ft int
.Fn pmc_rw "pmc_id_t pmc" "pmc_value_t newvalue" "pmc_value_t *oldvaluep"
.Ft int
.Fn pmc_write "pmc_id_t pmc" "pmc_value_t value"
.Sh DESCRIPTION
These functions read and write the current value of a PMC.
.Pp
Function
.Fn pmc_read
will read the current value of the PMC specified by argument
.Fa pmc
and write it to the location specified by argument
.Fa value .
.Pp
Function
.Fn pmc_write
will set the current value of the PMC specified by argument
.Fa pmc
to the value specified by argument
.Fa value .
.Pp
Function
.Fn pmc_rw
combines a read and a write into a single atomic operation.
.Pp
For write operations the PMC should be a quiescent state.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
A call to these functions may fail with the following errors:
.Bl -tag -width Er
.It Bq Er EBUSY
A write operation specified a currently running PMC.
.It Bq Er EINVAL
Argument
.Fa pmc
specified a PMC not in a readable state.
.It Bq Er EINVAL
The PMC specified by argument
.Fa pmc
was not owned by the current process.
.El
.Sh SEE ALSO
.Xr pmc 3 ,
.Xr hwpmc 4
